With the increased emphasis in weight reduction of the automobile, the master cylinder reservoir of the hydraulic brake system of at least one well known make of automobile is now being made of a relatively fragile plastic type material which should not be subjected to the clamping or fluid pressures to which prior master cylinder reservoirs have been heretofore subjected during power bleeding of the hydraulic brake system. Such prior reservoirs were fabricated of cast iron or other sufficiently tough material that they could withstand clamping or fluid pressures without danger of fracture.